why averaging only 4MB/s and how to spare bad blocks?

[sjs]

OK.
Just an update:

As you predicted, it didnt work (at first):

| 07:16:29 PM | Info | ......COMMAND => Verifying that permissions are enabled for demo
| 07:16:29 PM | Error | Could not enable permissions for volume demo : please restart your Macintosh

so i do
#mv demo.sparseimage demo.sparseimage.orig
and the error changed to:

| 07:17:43 PM | Info | hdiutil: create failed - Permission denied
| 07:17:43 PM | Error | ****FAILED****: result=256 errno=22 (Unknown error: 0)

looking at the perms one level up i see:
dr-x------ 3 demo demo 102 Mar 20 19:17 .
drwxrwxr-t 10 root admin 340 Mar 17 06:12 ..
-rwx------ 1 demo demo 9484529664 Mar 17 06:12 demo.sparseimage.orig

so i do:
#chmod u+w .

and now.... it works!

well, is this what you mean by not working? that it wouldnt start the copy?
b/c i dont know if the resultant copy with be a "valid filefault", but i am 99% sure it will, unless u know something i dont.